Shield Block disabled in arena or?

[Watamote]

So I have been experimenting with Prot warrior in arena, and I notice one crucial ability just doesn't work at all while in arena. I can use it outside arena just fine. I can even use it in the arena lobby. But when the arena actually starts, it becomes greyed out and unusable. Not sure if this is intentional or what.

[thechazas]

Of course it is not intended.